1. Field of the Invention
The present invention relates to a device for driving a recording head that conducts recordings on a record medium, and also to a recording apparatus.
2. Description of Related Art
Various types are known as a recording head that conducts recording on a record medium. A mentionable example thereof is an ink-jet head that performs printing by ejecting ink through a large number of nozzles. Some ink-jet heads change the amount of ink ejected through the respective nozzles during one printing cycle, to thereby achieve gradation printing.
For example, Japanese Patent Unexamined Publication No. 2000-158643 discloses that transmitted from a main circuit of an ink-jet recording apparatus to a head driver are a plurality of waveform signals that are to be used for performing gradation printing and select data sets that include a predetermined number of bits and correspond to respective nozzles and also to any one of the plurality of waveform signals. In the head driver, a predetermined one of the plurality of waveform signals is selected for every nozzle based on the select data set corresponding to that nozzle. Ink is ejected through the nozzle in accordance with the waveform signal thus selected. In a case where, for example, four waveform signals that correspond to respective four ink-ejection mode (e.g., four cases where the ink ejection amount is zero, small, middle, and large) are transmitted to the head driver, the select data set which is used for selecting, for each nozzle, any one of these four waveform signals is constituted of two-bit data in order to have one-to-one correspondence with the four waveform signals. Here, the ink ejection amount being zero means no ink ejection performed.
In many cases, the number of signal lines through which the select data sets are serially transmitted from the main circuit to the head driver is the same as the number of bits included in the select data set, because it simplifies circuitries. For example, two signal lines are adopted in order to transmit two-bit select data set to the head driver, and three signal lines are adopted in order to transmit three-bit select data set to the head driver.
The number of nozzles has seen a recent trend of considerable increase in order to meet a demand for high-quality and high-speed printings. In addition, there arises a need of increasing the number of waveform signals for the purpose of performing a multi-gradation printing to thereby improve print quality. An increase in the number of waveform signals inevitably involves an increase in the number of bits included in a select data set that is to be used for selecting, for each nozzle, any one of a plurality of waveform signals. Thus, not only nozzles but also bits included in a select data set for each nozzle are increased in number. As a result, the select data transmitted from a main body to a head driver of a recording apparatus include a considerably increased number of bits in total. When, like this, the total number of bits included in the transmitted select data is increased, a longer transmission time is required. This causes difficulty in high-speed printing which should have been an original object. However, when the select data are transmitted at a higher rate (i.e., when a clock signal applied for every transmission has a higher frequency) for the purpose of high-speed printing, signal lines emit more noise during transmission, to adversely affect peripheral devices of the recording apparatus.